The present invention relates to an ink-jet head for ejecting ink droplets from each ink pressurizing cell for imparting a pressure pulse to the ink pressurizing cell and, more particularly, a sidewall of the ink pressurizing cell for imparting a pressure pulse jto the ink pressurizing cell by means of shear mode deformation. The present invention also relates to a manufacturing method of the ink-jet head.
In general, conventional ink-jet heads used in ink-jet recording devices utilized thermal jet systems whereby air bubbles were generated in the ink pressurizing cells by heating elements to thereby pressurize the ink in the ink pressurizing cells (refer to Japanese Patent Kokoku Publication No. 59914/1986). However, in this case, since the ink is heated by the heating elements, the ink is impaired by the heat and printing quality is reduced. Also, since air bubble generation cannot be stabilized, clogging of the orifices occurs, air bubbles enter an ink flow path, and thermal stress produces cracks in the composing parts of the ink-jet head.
An alternative ink-jet head utilizing piezoelectric material is disclosed in, for example, U.S. Pat. No. 5,227,813 and 5,235,352. FIG. 1 shows a cross-sectional view of a main part of the ink-jet head disclosed in the above-mentioned publications. As shown in FIG. 1, the ink-jet head comprises a plurality of ink pressurizing cells or channels 14a, 14b, . . . defined by a bottom part 1, sidewalls 2, a top part 3 and a front wall having a plurality of orifices 15a, 15b, . . .
The bottom part 1 is formed from a lower part of a piezoelectric material base 11 polarized in an array direction P.
Each sidewall 2 comprises a projecting wall section 11a (or 11b, . . . ) which is composed of an upper part of a piezoelectric material base 11, and an intermediate wall section 12a (or 12b, . . . ) made from piezoelectric material polarized in the same direction P as that of the piezoelectric material base 11 and disposed on the projecting wall section 11a (or 11b, . . . ). Electrodes 16a, 16b, . . . are respectively formed at the ends of the projecting wall sections 11a, 11b, . . . Electrodes 17a, 17b, . . . and electrodes 18a, 18b, . . . are formed at the respective ends of the intermediate wall sections 12a, 12b, . . . Conductive adhesives 20a, 20b, . . . are disposed between the electrodes 16a, 16b, . . . and the electrodes 17a, 17b, . . . The intermediate wall sections 12a, 12b, . . . are secured to the projecting wall sections 11a, 11b, . . . of the piezoelectric material base 11 by the conductive adhesive 20a, 20b, . . .
The top part 3 comprises a top plate 13 and a common electrode 19 formed on a lower surface of the top plate 13. Conductive adhesives 21a, 21b, . . . are disposed between the common electrode 19 and the electrodes 18a, 18b, . . . of the intermediate wall sections 12a, 12b, . . . The top plate 13 is secured to the intermediate wall sections 12a, 12b, . . . by the conductive adhesive 21a, 21b, . . .
When the common electrode 19 is grounded, a positive voltage +V is applied to the electrode 16a and a negative voltage -V is applied to the electrode 16b, an electric field is generated through the piezoelectric element base 11 from the projecting wall section 11a to the projecting wall section 11b in the direction shown by a broken line A. Also, an electric field is generated in the intermediate wall section 12b from the electrode 17a toward the common electrode 19 in the direction shown by a broken line B. Also, an electric field is generated in the intermediate wall section 12b from the common electrode 19 toward the electrode 17b in the direction shown by a broken line C. As a result, shear mode deformation (shown by broken lines 60 in FIG. 1) is generated in respectively opposite directions in the projecting wall sections 11a, 11b and the intermediate wall section 12a, 12b. The ink in the ink pressurizing cell 14a is then pressurized, and ink droplets are ejected from the orifice 15a.
In this case, leak current in the direction D flows in the ink pressurizing cell 14a from the electrode 20a to the electrode 20b, the amount of pressurization in the ink pressurizing cell 14a by shear mode deformation is reduced, and an adequate amount of ink droplets cannot be ejected from the orifice 15a. In addition, electrochemical reaction caused by the leak current produces corrosion in the electrodes 16a, 16b and 17a, 17b and the ink quality can be impaired.
As indicated by the double dotted line in the ink pressurizing cell 14b, a method can be considered whereby parts of the piezoelectric material base 11 and the intermediate wall sections 12b, 12c contacting the ink are covered with an insulated coating layer 24, thereby insulating an interior of the ink pressurizing cell 14b from the electrodes 16b, 16c and 17b, 17c.
However, the width of the ink pressurizing cell is set very narrow at 30-100 [.mu.m], making uniform and complete covering by the insulated coating layer 24 difficult. Also, since burrs are easily produced in the end faces of the electrodes 16b, 16c and 17b, 17c when forming the grooves (ink pressurizing cells), pinholes are produced in the insulated coating layer 24, preventing insulation of the ink pressurizing cell 14b from the electrodes 16b, 16c and 17b, 17c.